N. Maity, S. Barman,E. Callens, M. K. Samantaray, E. Abou-Hamad, Y. Minenkov, V. D'Elia, A. S. Hoffman, C. M. Widdifield, L. Cavallo, B. C. Gates and Jean. Basset
Chem. Sci., 7, 1558-1568, (2016)
The well-defined single-site silica-supported tungsten complex [(Si–O–)W(Me)5], 1, is an excellent precatalyst for alkane metathesis. The unique structure of 1 allows the synthesis of unprecedented tungsten hydrido methyl surface complexes via a controlled hydrogenolysis. Specifically, in the presence of molecular hydrogen, 1 is quickly transformed at −78 °C into a partially alkylated tungsten hydride, 4, as characterized by 1H solid-state NMR and IR spectroscopies. Species 4,
upon warming to 150 °C, displays the highest catalytic activity for
propane metathesis yet reported. DFT calculations using model systems
support the formation of [(Si–O–)WH3(Me)2],
as the predominant species at −78 °C following several elementary steps
of hydrogen addition (by σ-bond metathesis or α-hydrogen transfer).
Rearrangement of 4 occuring between −78 °C and room temperature leads to the formation of an unique methylidene tungsten hydride [(Si–O–)WH3(CH2)], as determined by solid-state 1H and 13C
NMR spectroscopies and supported by DFT. Thus for the first time, a
coordination sphere that incorporates both carbene and hydride
functionalities has been observed.